In recent years, in the field of display units displaying an image, display units using, as light-emitting devices of pixels, current drive type light-emitting devices of which light emission luminance changes with a value of a current flowing therethrough, for example, organic EL devices have been developed for commercialization. Unlike liquid crystal devices and the like, the organic EL devices are self-luminous devices. Therefore, in a display unit (an organic EL display unit) using the organic EL devices, since a light source (a backlight) is not necessary, compared to a liquid crystal display unit needing a light source, a reduction in thickness of the display unit and an increase in luminance of the display unit are achievable. In particular, in a case where the display unit uses an active matrix system as a drive system, each pixel is allowed to continuously emit light, and a reduction in power consumption is achievable. Therefore, the organic EL display unit is expected to become a mainstream of next-generation flat panel display.
Incidentally, current-voltage (I-V) characteristics of a typical organic EL device deteriorate with the lapse of time (deteriorate with time). In a pixel circuit that drives the organic EL device with a current, when the I-V characteristics of the organic EL device change with time, a division ratio between the organic EL device and a drive transistor connected in series to the organic EL device changes; therefore, a gate-source voltage of the drive transistor also changes. As a result, a value of a current flowing through the drive transistor changes; therefore, a value of a current flowing through the organic EL device voltage also changes, and light emission luminance also changes with the current value accordingly.
Moreover, a threshold voltage (Vth) or mobility (μ) of the drive transistor may change with time, or Vth or μ may differ for each pixel circuit due to variation in manufacturing processes. In a case where Vth or μ of the drive transistor differs for each pixel circuit, the value of the current flowing through the drive transistor varies for each pixel circuit; therefore, even if a same voltage is applied to a gate of the drive transistor, light emission luminance of the organic EL device varies, and uniformity of a screen is impaired.
Therefore, even if the I-V characteristics of the organic EL device change with time, or Vth or μ changes with time, to keep light emission luminance of the organic EL device constant without being affected by them, a display unit having a compensation function for variation in the I-V characteristics of the organic EL device and a correction function for variation in Vth or μ has been developed (for example, refer to PTL 1).